1. Field of the Invention
The present invention relates to a deflection compensation roll with a roll jacket which is arranged on antifriction bearings in the area of its axial ends and is hydraulically supported parallel to a working plane.
2. Discussion of Background Information
Such a deflection compensation roll is known from DE 198 54 339 A1. Rolls of this kind are preferred for use as end rolls in a calender for glazing a paper web or another material web, i.e., to impinge in the nips of the calender with increased pressure, if necessary also at increased temperature. In addition to the antifriction bearings, the known roll features a hydrostatic support element that is designed to guarantee a minimum load on the antifriction bearings. This is intended to make it possible for an additional force to be exerted that is sufficient for an orderly rolling entrainment of the roll bodies of the antifriction bearing.
DE 198 33 308 A1 shows another deflection compensation roll with hydrostatic support elements that work offset by 90° to the working plane. These support elements are used to position the jacket. They are supported on a carrier that follows a movement of the support elements in the working plane. There is a mechanical connection for this between the carrier of the transverse support elements and the support elements in the active direction.
A further deflection compensation roll is known from EP 0 764 790 B1. In this case the forces necessary for the support are applied by using two rows of opposing support rolls, between which the angle is smaller than 180°.
EP 0 772 715 B1 describes the use of a roll with “spreading elements” at the roll end, i.e., hydraulic support elements which exert forces acting on the inner circumference of the end of the hollow cylinder crosswise to the working plane and pull the end of the hollow cylinder apart, so to speak, relative to the working plane, causing the hollow cylinder to be pulled away in the nip at the end of the nip.
As mentioned at the outset, such deflection compensation rolls are preferred for use in calenders for treating paper webs. The operating speed of such calenders has been consistently increased over recent years. However, the increase in the operating speed also entails an increase in the rotational speed of the roll jacket. This leads to the roll jacket reaching critical speed ranges where there is a danger of a resonance phenomenon. Since such resonances can be calculated beforehand, in most cases it is possible to take remedial action.
It has now been shown with some rolls that undesirable vibrations occur at rotational speeds at which they would not normally have been expected. In particular, an inherent frequency of the roll jacket has been observed far below its first inherent deflection frequency. Such a resonance vibration is possibly also one of the causes of the formation of so-called barring, in which transverse stripes occur on the paper web during glazing which, when they become visible, lead to the paper web being discarded.